1. Field of the Invention
The present invention is directed to the field of processing data from electronic light sensors that are directly exposed to a scene or that are exposed to film that has captured the scene.
2. Description of the Related Art
Photographic film is often able to capture in a single exposure the full dynamic range of a scene, which can often have a range of up to one million to one. However, this full dynamic range may not be communicated to the viewer through conventional optical and digital techniques.
Fortunately, because of the nature of photographic film and because of its wide latitude, it is possible to scan the developed film negative using an electronic photosensitive or charge coupled device (“CCD”) sensor. Although the CCD used in the scanner is based on conventional electronic sensor technology, this arrangement of film scanning can capture the entire dynamic range of the scene. The ability to capture over 16 stops (where a stop corresponds to a two-to-one increase in light level) has been demonstrated. The issue with film is shown in FIG. 37 where, for different colors, while the response may be consistent within normal intensity ranges, the response may differ at extreme ranges of highlights. Notice that FIG. 37 is plotted as the logarithmic to the base 10 of intensity E of the scene against the data value from the AND of the film scanner after passing through a look up table to produce, for example, density values of the film.
CCDs and other electronic scene sensors generate image signals by producing an electron signal that is generally converted into an output voltage. CCDs for example, produce an electron charge generated by photons that impinge on the sensor area of the CCD or other electronic sensor. Consequently, this imaging process is fundamentally linear with light intensity for a fixed exposure time (and integrated light energy for a variable exposure time). Because of this linear nature, typical electronic images have a dynamic range of about one thousand-to-one. However, a scene can also have specular highlights with a range of up to one million-to-one or greater. Accurate reproduction of both the color and structure of these highlights is required if a scene is to be accurately reproduced.
What is needed and the problem to be solved is the provision of a system for increasing the dynamic range of an electronic image sensor and the ability to ensure that, for a film-based system, the scene is accurately captured over its entire range.